In general, vehicle ultrasonic sensors may be classified into an ultrasonic sensor for parking assistance, an ultrasonic sensor for automatic parking assistance, and an ultrasonic senor for blind spot detection according to the purpose of use.
An ultrasonic sensor for parking assistance operates when the velocity of a vehicle is equal to or less than 10 km/h, and an ultrasonic sensor for automatic parking assistance operates when the velocity of a vehicle is less than 35 km/h. The ultrasonic sensors are configured to sense static objects.
An ultrasonic senor for blind spot detection operates when the velocity of a vehicle is equal to or greater than 30 km/h, and is configured to sense dynamic objects, that is, opponent vehicles. That is, the ultrasonic senor for blind spot detection senses an opponent vehicle that travels in a blind spot and has a relative velocity of up to ±20 km/h.
The aforementioned ultrasonic sensor for parking assistance uses a band pass filter having a small bandwidth in order to be robust to acoustic noise because the frequency of a transmission signal is equal to the frequency of a reception signal that is reflected by an object to be sensed and received.
In addition, for the ultrasonic sensor for automatic parking assistance, although a vehicle may travel at up to 35 km/h, a moving line of the vehicle is perpendicular to a location of an object, and thus the frequency of a transmission signal is equal to the frequency of a reception signal.
That is, in general, since the ultrasonic sensor for parking assistance or the ultrasonic sensor for automatic parking assistance senses a static object, the frequency of the transmission signal is equal to the frequency of the reception signal. Accordingly, the ultrasonic sensor for parking assistance or the ultrasonic sensor for automatic parking assistance uses a band pass filter having a small bandwidth in order to be robust to external acoustic noise or electric noise. That is, since the bandwidth of the band pass filter is proportional to implementation complexity, a band pass filter having the smallest bandwidth within a given price range is chosen as a band pass filter of the ultrasonic sensor for parking assistance or the ultrasonic sensor for automatic parking assistance.
However, an ultrasonic senor for blind spot detection senses a dynamic object (e.g., an opponent vehicle) in a blind spot, and a relative velocity with respect to an opponent vehicle may be up to 20 km/h. Accordingly, due to the Doppler effect, the frequency of the transmission signal is not equal to the frequency of the reception signal.
Accordingly, when an ultrasonic senor for blind spot detection uses a band pass filter having a small bandwidth, such as that of the aforementioned acoustic sensor for parking assistance or acoustic sensor for auto-parking assistance, the filter may attenuate signals reflected by opponent vehicles as well as noise (e.g., ground signals).
When a band pass filter having a large bandwidth is used to solve the above problem, the ultrasonic sensor for blind spot detection may misrecognize signals (i.e., noise) reflected from the ground as an object sensed in a blind spot and provide a false alarm because the velocity of 30 km/h or greater causes the Doppler effect.
When an ultrasonic sensor is used to sense the rear to assist with parking rather than sensing a blind spot, the ultrasonic sensor may have a vertical beam angle that is set to be wide in order to sense speed humps. Accordingly, on a condition that the ultrasonic sensor having the wide vertical beam angle operates to sense a blind spot, when a ground signal is sensed from a remote location where magnitude of a signal of another vehicle decreases, it is difficult for the ultrasonic sensor to distinguish between the ground signal and the signal of the other vehicle.